Contador has been provisionally suspended by the International Cycling Union after a trace of the banned substance clenbuterol was discovered in his urine sample taken at the Tour in July.

"I know Alberto, I've worked with him for three years. I personally cannot believe he is guilty," Bruyneel, who managed Contador at the Discovery Channel and Astana teams, said on Thursday. "I think it's perfectly possible that his positive result would be due to a contaminated piece of meat or whatever supplement, but then again the result is that A and B sample show up positive.

"Now it's up to the authorities to deal with it and I think it's a very sensitive matter because it is possible to have a positive (test) if you haven't done anything. I am convinced about that. So I would feel really bad for him if this would be the case that he would get suspension or even a reduced suspension."

Bruyneel, who now manages Lance Armstrong's RadioShack, had to fire Chinese rider Li Fuyu in August after a B sample came back positive for clenbuterol, an anabolic agent that can be used to reduce body fat.

"I have no doubts (about Contador) because I had a similar case in May with a Chinese rider on my team," Bruyneel said. "It's exactly the same quantity (as Contador) which is the least amount that can be measured and I'm pretty sure that's the same case, but I had to terminate his contract.

"A test is a test and if there is a small quantity there, it's there. I think you have to be able to make the difference if it was deliberately ingested or if it was there because he ate a contaminated piece of meat. I am pretty sure there are more athletes that have been convicted and are in the same case."

The UCI said Contador's clenbuterol was detected on July 21, the Tour's final rest day. A urine sample taken from Contador the following day also showed abnormally high levels of plastic residues that could indicate he received a transfusion of his own blood during this year's race, a person with knowledge of the test results told the AP on Tuesday.

"I think it's irrelevant because I don't think it's part of the problem," Bruyneel said after speaking at the Leaders in Performance conference in London where his session was closed to the media. "I think the facts are there were 50 (picograms) of clenbuterol in his sample and that has to be explained.

"And I think everything else is irrelevant. From what I hear, these tests are not validated yet."

Contador has challenged cycling authorities to freeze his urine and blood samples until technology can show he rode clean in this year's race.

Bruyneel could also agree to having all of his RadioShack riders' frozen samples tested before using the plastics test if the detection method